Dual fueling engine systems with direct and port fuel injectors may be configured to operate under a wide range of engine operating conditions. For example, at higher engine speeds and loads, fuel may be directly injected into engine cylinders to increase engine torque and enhance cooling of cylinder charge mixtures while minimizing chances of engine knock. At lower engine speeds and loads, fuel may be injected via port fuel injection to reduce particulate matter emissions. Specifically, port injected fuel may quickly evaporate as fuel is drawn into an engine cylinder, reducing particulate matter buildup while improving fuel efficiency. Fuel may be injected into an engine via both direct and port fuel injection during mid-speeds and loads in order to improve combustion stability and reduce engine emissions. Therefore, an engine with direct injectors (DI) and port fuel injectors (PFI) can leverage the advantages of each individual injection type.
While it may be beneficial to incorporate port and direct fuel injectors into an engine, supplying fuel via two different injection systems may make it difficult to distinguish injection errors resulting from the port injector from those resulting from the direct injector. One example approach for determining which fuel injection source is introducing fueling errors into the engine is shown by Surnilla et al in US20160131072. Therein, port and direct fuel injector errors are determined by calculating a ratio of a change in fuel multiplier values and a change in fraction of fuel injected into engine via port and direct injection, wherein fuel multiplier values are determined based on a measured air-fuel ratio. A port injector error is determined by calculating a ratio of a change in fuel multiplier values and a change in fraction of port injected fuel, and a direct injector error is determined by calculating a ratio of change in fuel multiplier values and a change in fraction of directly injected fuel.
However, the inventors herein have recognized potential issues with such an approach. As one example, the approach is not able to distinguish fueling errors of direct and port fuel injectors from a common error. The common error may include a common fuel type error and/or an air error. A common fuel type error may occur when quality of a fuel degrades. For example, changes in fuel viscosity may cause both port and direct fuel injectors to provide a lower or a larger fuel amount than expected, causing a common fuel type error. Alternatively, a common fuel type error may occur when the actual fuel injected into engine is different from the expected fuel, such as when the oxygen content of a fuel injected into a flex fuel engine deviates from the oxygen content of the fuel refilled into the fuel tank. On the other hand, a common error may be an air error caused by a degraded engine sensor such as mass air flow sensor, a pressure sensor or a throttle position sensor. Alternatively, an air error in a multi-cylinder engine may occur if some engine cylinders receive more air than other cylinders due to location of the cylinders along an intake air passage or due to a configuration of the intake passage. An engine controller may correct for the port or direct injector error by adjusting a transfer function of the injector. Additionally, the degraded injector may be disabled. However, if the air-fuel error is due to a common error, the air-fuel error may persist even after the transfer function is adjusted based on an injector error. Furthermore, a fuel injector may be disabled even if it is not degraded, as a result of which the advantages of that particular injection type may not be leveraged.
In one example, the issues described above may be addressed by a method for fueling an engine, comprising: injecting fuel to a cylinder via a first fuel injector and a second fuel injector; and distinguishing an error associated with the first fuel injector or the second fuel injector from a common fuel system error as a function of a rate of change of air-fuel ratio error and a fraction of fuel injected via the first fuel injector or the second fuel injector. By separating individual fueling errors of direct injectors and port fuel injectors from the common error, engine performance and exhaust emissions are improved.
For example, an air-fuel error may be determined in an engine fueled via both direct and port fuel injection as a difference between an actual air-fuel ratio (determined at an exhaust gas sensor) and an expected air-fuel ratio. A ratio of rate of change of the air-fuel error to a rate of change of fraction of directly injected or port injected fuel is a fueling slope error between direct and port fuel injection systems. If a fueling slope error difference between the DI and PFI fuel systems is higher than a threshold slope error, then either of the fuel system is faulted rich or lean. The absolute fueling slope error for the DI fueling system can be adapted and if this value is higher than the threshold slope error then the direct injection system is faulted rich or lean. Similarly, the absolute fueling slope error for the PFI fueling system can be adapted and if this value is higher than the threshold slope error then the port injection fueling system is faulted rich or lean. If the fueling slope error changes by a small magnitude during engine operation, but the air-fuel errors corresponding to different engine speed-load conditions are higher than a threshold air-fuel error and with same directionality (irrespective of the direct or port fuel injection fuel system), the slope error may be attributed to a common error. Subsequently, distinct error mitigating actions may be taken based on whether the identified error was due to the direct injector, the port injector, or the common error. For example, distinct transfer function compensations may be applied.
The approach described herein may confer several advantages. In particular, the approach allows errors that are common to both fueling systems to be learned distinct from fueling errors of individual direct and port fuel injectors. Further, the common errors may be compensated for differently than the direct and port fuel injector errors. By separating individual fueling errors of the direct and port fuel injectors from the common error, air-fuel imbalances can be better addressed. Further, the approach may reduce the erroneous disabling of non-degraded fuel injectors.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.